Wearable personal hydration systems are used by athletes, recreationalists, workers, military personnel, and others, to provide convenient access to fluid while in action. For activities requiring more than a liter of fluid, for example, a soft-sided fluid reservoir carried in a backpack or waistpack is often used. Hydration systems such as this can consist of a pack and a soft-sided reservoir paired with a flexible drink tube ending in a closable mouthpiece. Fluid capacities for pack-mounted reservoirs typically range from 1 to 3 liters. They feature a sealable fill port and an exit port at the base of the reservoir which connects to the drink tube. Fill and exit ports can be integrated into the edge of the soft-sided reservoir or more commonly, sealably attached to the reservoir's flat top surface. The drink tube ends in a mouthpiece which can be activated by the user to initiate fluid flow.
Pack-mounted bladders can have a number of strengths in regards to providing fluid access for longer-term physical activity. The reservoirs can be light in weight, yet durable. With their soft sides they can be relatively comfortable to wear and they have the added benefit of collapsing flat when they are empty. Their collapsibility also helps minimize fluid sloshing. The mouthpiece can be tethered to the chest area for easy access and drinking can be largely hands-free.
While bladder-based hydration systems offer plenty of fluid to replenish long distance runners and cyclists, for example, single chamber bladders mean that only one kind of fluid can be carried at a time. If an athlete wishes to carry an electrolyte type fluid they either need to fill the bladder with electrolyte or carry it separately in a bottle or second hydration bladder.